Stereoscopic photography has been practiced since almost the beginning of photography itself. Early stereoscopic viewers allowed users to view scenic locations with a realism lacking in ordinary photography. Modern versions of stereoscopic viewers, such as the View-Master, produced by Tyco Toys, have long been staples of the toy industry. Advances in technology have produced such variations as "3-D" movies and, more recently, "virtual reality," or computer generated interactive stereoscopic simulations. As real-time stereoscopic viewers are beginning to find uses in such areas as the medical field, it is apparent that stereoscopic viewing is becoming more common.
The optical phenomenon exploited by the brain to extract depth information from a three dimensional scene is known as "parallax." As shown in FIG. 1, a person with two functional eyes 402 viewing point 304 sees slightly different images in each eye 402, due to the slightly different angle from each eye 402 to point 304. The apparent location of point 304 is different for each eye 402. By analyzing the differences due to parallax, the brain is able to determine the distance to point 304. By photographing, or otherwise recording, a scene from two distinct locations which mimic the location of eyes 402, as illustrated in FIG. 2, a set of images can be generated which, when viewed properly, can recreate the parallax of the original scene, giving the illusion of three dimensions in the two dimensional images. Each camera 202 uses lens 204 to project an image of point 304 onto image plane 308. As illustrated in FIGS. 3a and 3b, each image point 302 of images 300a and 300b represents a point 304 in a three dimensional scene. Each image 300 is associated with a "vantage point" 306, which is the location of the point of view of that image 300. Each image point 302 corresponds to the intersection of an image plane 308 with a "view line" 310. A view line 310 passes through a vantage point 306 and the point 304 in the scene which is represented by image point 302. The view line 310 which passes through vantage point 306 and intersects image plane 308 perpendicularly defines a "center point" 312 in the image 300 associated with the vantage point 306.
A set of two or more images 300 is "stereoscopic" if they represent substantially parallel views of substantially the same scene, with the vantage points 306 of the images 300 being separated in a direction substantially perpendicular to the direction of the views, this perpendicular direction defining the "epipolar" axis 314.
As illustrated in FIG. 4, when stereoscopic images 300 are viewed with eyes 402 taking the place of vantage points 306 relative to images 300, the viewer perceives apparent points 404 where points 304 had been.
There are a number of reasons one might wish to change the apparent depth 416 of at least some of the apparent points 404 in a set of stereoscopic images 300. Some viewers of images 300 may experience vertigo or nausea due to extremes in the apparent depth 416 of apparent points 404 and need to have the apparent depth 416 moderated. Others may aesthetically prefer the sensation of extremes in depth, and may wish to have the apparent depth 416 in a set of stereoscopic images 300 augmented. Still others may wish to create a new scene in which particular apparent points 404 are brought forward to focus attention on them.
The apparent depth 416 of apparent points 404 in a stereoscopic set of images 300 is controlled by three factors: 1) the actual depth 316 of points 304 represented, 2) the ratio of distance 420 between each of the viewer's eyes 402 to distance 320 between vantage points 306a and 306b, and 3) the ratio of distance 318 between vantage points 306 and image plane 308 and distance 418 between the viewer's eyes 402 and images 300.
After images 300 have been recorded or created, only the third factor can conventionally be changed, by changing distance 418 between the viewer's eyes 402 and images 300. By changing this distance, the apparent depth 416 of all points 404 in the scene can be altered. Doing this, however, is often impossible or inconvenient, since the viewing apparatus may not allow for altering distance 418. Also, changing distance 418 without changing the magnification alters the apparent distance between points 404 in the scene, as well as the apparent field of view. Changing the magnification of images to account for the changes due to changes in distance 418 negates the changes to apparent depth 416. Finally, changing distance 418 does not allow the apparent depth 416 of points 404 to be individually changed on a point-by-point basis.
What is needed is a system and method for modifying the apparent depth of points 404 in a set of stereoscopic images 300 in a way which does not affect the apparent depth 416 of other points 404, and which does not require alteration of distance 418.